Promote SkInterpolator unit test to our tests driver.

gyp/tests.gypi

 # Common gypi for unit tests.
 {
   'include_dirs': [
     '../src/core',
     '../src/effects',
     '../src/image',
     '../src/lazy',
     '../src/images',
     '../src/pathops',
     '../src/pdf',
@@ skipping 84 matching lines @@
     '../tests/GrRedBlackTreeTest.cpp',
     '../tests/GrOrderedSetTest.cpp',
     '../tests/GrSurfaceTest.cpp',
     '../tests/GrTBSearchTest.cpp',
     '../tests/GradientTest.cpp',
     '../tests/HashCacheTest.cpp',
     '../tests/ImageCacheTest.cpp',
     '../tests/ImageDecodingTest.cpp',
     '../tests/ImageFilterTest.cpp',
     '../tests/InfRectTest.cpp',
+    '../tests/InterpolatorTest.cpp',
     '../tests/JpegTest.cpp',
     '../tests/KtxTest.cpp',
     '../tests/LListTest.cpp',
     '../tests/LayerDrawLooperTest.cpp',
     '../tests/LayerRasterizerTest.cpp',
     '../tests/MD5Test.cpp',
     '../tests/MallocPixelRefTest.cpp',
     '../tests/MathTest.cpp',
     '../tests/Matrix44Test.cpp',
     '../tests/MatrixClipCollapseTest.cpp',
@@ skipping 78 matching lines @@
     '../src/utils/debugger/SkObjectParser.h',
     '../src/utils/debugger/SkObjectParser.cpp',
 
     '../tests/PipeTest.cpp',
     '../src/pipe/utils/SamplePipeControllers.cpp',
 
     '../tests/TDStackNesterTest.cpp',
     '../experimental/PdfViewer/src/SkTDStackNester.h',
   ],
 }